One of the possible clasification of the particles is according to its spins. If its spin is an integer, then we call it a 'boson' and the wavefunction that describes its behavior is symmetric. If its spin is a semi integer, then we call it a 'fermion' and its wavefunction is antisymmetric.

The first kind of particles doesn't obey Pauli Exclusion Principle (two particles can't be in the same individual quantum state) so them can stand in the same state.

When we cool a boson system under a characteristic temperature, the more energetic particles begin to 'fall' in the lowest energy state, to minimize its energy. If we continue cooling and cooling the system, then all the system will be in the lowest energy state.

Then, particles are quiet.

Condensation has not the same meaning that usual condensation. When we say that vapour condensates, we mean that it reduces its volume, then rises its density and so. In BEC, the particles can remain the same volume, the same density. But in BEC particles are quiet.